1. Technical Field
The present disclosure relates to transistors in integrated circuits and, more particularly, to thin film transistors having metal in the channel region.
2. Description of the Related Art
Integrated circuits are used in a large variety of applications. Individual integrated circuits can take the form of voltage amplifiers, voltage regulators, digital signal processors, microcontrollers, wireless adapters, microprocessors, smart cards, and many other devices. Some integrated circuits have circuitry that performs many of these functions on a single chip.
The transistor is the fundamental building block of most integrated circuits. Digital integrated circuits generally use large numbers of transistors as switches to perform all manner of computing operations. The larger the number of transistors, the more complex and powerful an integrated circuit can be. The miniaturization of the transistor in integrated circuits has allowed for billions of transistors to be formed in individual integrated circuits. The complex arrangement of so many transistors has allowed for powerful yet small electronic devices to be manufactured.
The transistor is also used as an analog device in integrated circuits. For instance, the trandsconductance characteristics of transistors allows them to be used as signal amplifiers. A small change in voltage at one terminal of a transistor can lead to a relatively large change in current flowing between other terminals of the transistor. Transistors are used in circuits with passive analog circuit elements such as resistors, capacitors, and inductors to form powerful and complex analog electronic devices.
In current technology, transistors are generally formed at the surface region of a monocrystalline semiconductor substrate. The channel region of each transistor is formed in the single crystal semiconductor substrate. The surface area of the substrate is a limiting factor in the number of transistors that can be formed at the surface of the substrate. Monocrystalline semiconductor substrates are expensive to form and are limited in size.
Physical limitations will eventually halt the miniaturization of transistors at the surface of semiconductor substrates. Due to the expense and difficulty in forming large monocrystalline semiconductor substrates, simply increasing the area of the semiconductor substrate leads to increased cost of the integrated circuit.